Transcription disc

A transcription disc is a special phonograph record intended for, or recorded from, a radio broadcast. Sometimes called a broadcast transcription or radio transcription or nicknamed a platter, the official term was electrical transcription, usually abbreviated to E.T. among radio professionals.

Transcription discs are most commonly 16 inches (40 cm) in diameter and recorded at 33 1/3 rpm. That format was standard from approximately 1930 to 1960 and physically distinguishes most transcriptions from records intended for home use, which were rarely more than 12 inches (30 cm) in diameter and until 1948 were nearly all recorded at approximately 78 rpm. However, some very early (circa 1928-1931) radio programs were on sets of 12 inch (30 cm) or even 10 inch (25 cm) diameter 78 rpm discs, and some later (circa 1960-1985) syndicated radio programs were distributed on 12 inch (30 cm) diameter 33 1/3 rpm microgroove vinyl discs visually indistinguishable from ordinary records except by their label information.

Some unusual records which are not broadcast-related are sometimes mistakenly described as "transcription discs" because they were recorded on the so-called acetate recording blanks used for broadcast transcriptions or share some other physical characteristic with them. Transcription discs should not be confused with the 16 inch diameter, 33 1/3 rpm shellac soundtrack discs used from 1926 into the early 1930s to provide the audio for some motion picture sound systems. Also a potential source of confusion are RCA Victor's "Program Transcription" discs, 10 or 12 inch diameter 33 1/3 rpm records pressed in shellac and "Victrolac" vinyl in the early 1930s. Despite their suggestive name, they were not recorded from broadcasts or intended for broadcast use, but were an early and unsuccessful attempt to introduce longer-playing records at the 33 1/3 rpm speed for home use.

Transcription discs are of two basic types: pressings and instantaneous discs.

Pressings were created in the same way as ordinary records. A master recording was cut into a blank wax or acetate disc. This was electroplated to produce a metal stamper from which a number of identical discs were pressed in shellac or vinyl in a record press. Although the earliest transcription discs were pressed in shellac, in the mid-1930s quieter vinyl compounds were substituted. These discs were used to distribute syndicated programming to individual radio stations. Their use for this purpose persisted long after the advent of magnetic tape recording because it was cheaper to cut and plate a master disc and press 100 identical high-quality discs than to make 100 equally high-quality tape dubs.

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